Magnetic grid



Aug. 2, 1960 R. F. POST 2,947,902

MAGNETIC GRID Filed Aug. 20, 1959 2 Sheets-Sheet 1 33 INVENToR.

.I 347 BY R/CHARD F. Posr ATTORNEY.

Aug. 2, 1960 y R, F, POST 2,947,902

MAGNETIC GRID Filed Aug. 20, 1959 2 Sheets-Sheet 2 A T TORNE Y the* lackof same.

United States Patent 2,947,902 MAGNETIC GRID Richard F. Post, WalnutCreek, Calif., assig'uor to the 'United States of America as representedby the United States Atomic Energy Commission Filed Aug. zo, 1959, ser.No. 835,158

's claims. (Cl. 313-167) The present invention relates to an improvedelectronic grid adapted for use in the control of electrical dischargesin vacuum or gaseous atmospheres and, more particularly, to anelectronic grid employing magnetic forces for controlling the passage ofcharged particles.

This application is a continuation-in-part of my co- Patented Aug. 2,1960 and the applicability of the present invention is in no wiselimited to more conventional devices such as herebefore enumerated, thepresent invention being particularly useful in a device of the typedisclosed and claimed in'my copending patent application Serial No.816,351.

It is an object of the present invention to provide electric dischargecontrol means producing a magnetic field of a. configuration to controlby the magnitude thereof the passage of charged particles therethrough.

It is another object of the present invention to provide an electronicgrid producing a magnetic field of pending application Serial No.682,265, led September 5, 1957, now abandoned. p

Conventional grids or control electrodes employed in such as vacuum orgas tubes and more generically in any discharge device operate toproduce a desired electrostatic iield thereabout for applying forces ofdesired magnitude and direction to charged particles in the eld thereof.Such grid fields are produced by the application of a charge orpotential to the grid structure whereby the grid is surrounded by apredeterminable electrostatic eld. This conventional type of electronicgrid has found wide acceptance and is employed universally in thecontrol of electric discharges through space; however, certainfundamental limitations in this type of grid control have precluded theuse thereof under certain circumstances.

The aforementioned limitation of conventional electrostatic grid controlis based upon the fundamental characteristic of polarity found in allelectrostatic fields. -It is this liield polarity which provides theeffectiveness thereof and yet also results in the limitation upon theapplicability. Thus a negatively charged grid having a correspondingelectrostatic field thereabout operates to apply a repelling force toelectrons, in such as a discharge tube for example, land the magnitudeof the charge determines the magnitude of the force so as to control thenumber of electrons passing therethrough. However, in the instance suchas above where a gaseous atvmosphe're surrounds the grid, ionization ofthe gas by l electrons produces positively char-ged ions that are thusoppositely affected by the grid field, so as to be attracted toward thegrid. A certain number of such ions actual- -ly strike the grid toproduce a grid drain while many others attracted thereto form a sheathof positive charges about the grid to effectively cancel the grid eld sothat it no longer controls discharge. 'I'his phenomenon is Well knownand it is accepted in gaseous discharge devices, such as thyratrons,ignitrons, and the like, that grids are only operable to preventdischarge but exert no control thereover after discharge initiation andconsequent ion production. Further, conventional grids in gas tubes orthe like are ineffectual to cut olf the tube or cease tube conductionand it has been heretofore necessary to lower the plate potential to cutolf discharge in such devices.

It is widely appreciated in the electronic arts that great advantagewouldA lie in the provision of complete grid control of gaseousdischarge devices and', in fact, the applicability of such devices hasbeen limited Iby The present invention provides such a grid. Formerproblems of controlling and stopping gaseous discharges are obviated bythe present invention,

variable intensity for the control of charged particle passagetherethrough.

It is 'a further objectof the present invention to provide an electroniccontrol member employing magnetic rather than conventional electrostaticfields for controlling electricaldischarges.

It is yet another object of the present invention to provide anelectronic control electrode for similarly controlling the passage ofcharged particles of either polarity.

It is still another object of the present invention to provide a controlelectrode for gaseous discharge devices which retains control duringdischarge.

Numerous other advantages and possible `objects of the invention willbecome evident from the following description of a single preferredembodiment of the invention chosen for illustration and depicted in theaccompanying drawing, wherein:

Figure 1 is a plan view of an electronic grid embody- -ing the presentinvention;

Figure 2 is a schematic illustration of a portion'of the invention insection including a representative magnetic iield configuration depictedby dashed lines and charged particle paths indicated by dotted lines;

Figure 3 is a plan view of an alternative embodiment of the grid of thepresent invention; and

Figure 4 is a perspective view of an ignitron having the embodiment ofthe grid of Figure 3 mounted in operative position therein.

Considering now a simple embodiment of the invention and referring toFig. 1 of the drawing, there is provided as a grid structure 11 a planardouble spiral of electrically conducting Wire 12 or the like andcomprising an outer spiral 13 extending from an external terminal 14inward substantially to the center of a circle formed by the outerspiral turn. A second spiral 16 of wire is formed in the same plane asthe first and extending from the iirst spiral end at the centeroutwardly in equal spacing between turnsof the iirst spiral to a secondterminal 17 located outside the spirals. There will thus be seen to lbeformed a double spiral grid struc'- ture 11 wherein each turn of thesecond spiral is equally spaced from a pair of turns of the rst spiral.The wire 12 moreover is preferably of low resistance in order that aWide range of current magnitudes from zero to a relatively high valuemay Abe readily passed therethrough.

Energization ofthe grid is accomplished by a power vsupply 18 having apairof output terminals separately connected by leads 19 and 21 to thespiral terminals 14 and 17. This power supply will be seen to beconnected `across the ends of the double spiral so that the two seriallyconnected spirals 13 and 16 form a closed path between the power supplyterminals for current flowA therethrough. Provision is made for`controlling the amount of current owing through the grid, as for exampleby means integral with the power supply and controlled by a knob 22thereon or a rheostat 23 connected in circuit with the grid and powersupply.

Considering now the operation of the present invention, Iattention isfirst -invited to the fact that the grid itself comprises a pair ofconducto-rs disposed in spaced parallel relation and having currentflowing therethrough in opposition. The significance of this situationis best understood by reference to Fig. 2 wherein alternate conductorswill .be seen to carry current inthe same directions. Thus -in Fig. 2,wire 13 carries current rin one direction, say out of the plane of thedrawing, and alternate wire i6 carries current in the oppositedirection, sayV into the plane of the drawing. Current passing through awire establishes `a magnetic field encircling the'V Wire with the fielddirection being dependent upon thev direction of current flow so thateach wire is surrounded by a magnetic field, as illustrated by thedashed lines H in Fig. 2 and extending in the direction oi the arrowsthereon. It will be seen from Fig. 2 that as adjacent wire portionscarry current in opposite directions, the magnetic fields between eachwire `are additive.

As regards the action of the magnetic `fields established by the grid,consider a stream of charged particles 31 approaching the grid. As anymoving charged particle enters a magnetic lield, it is `acted upon by aresultant force perpendicular to the direction of particle motion andperpendicular to the magnetic field so that here it is seen that acharged particle entering the grid field is deflected. The degree ofparticle deflection is dependent in part upon the magnitude of themagnetic field and with a sufliciently strong field the particle losessubstantially all motion toward the grid and is in effect turned awayfrom the grid. As the magnitude of the magnetic field about a currentcarrying conductor decreases with distance from the conductor and isdetermined by the amplitude of the current in the conductor, it thusfollows that the field strength between grid conductors isV a functionof the current through these conductors. With a very low grid current,only `a weak magnetic iield exists between the grid conductors so thatcharged particles approaching the grid in any direction butsubstantially directly toward the conductors experience only a slightdeection so that they pass through the grid. Increasing the grid current4reinforces the magnetic eld about the conductors thereof so that alesser space' between coriductors is available for particle passagewithout such deilection as would prevent passage of the particlesthrough 'the grid. A still further increase in grid current additionallystrengthens the grid field until the field is suiiciently strong evendirectly between the grid conductors so that substantially fallapproaching charged particles are materially 1deflected and do not passthrough the grid, and the grid may be said to be at cut-off. Inasmuch asthe grid wire 12 is of low resistance, the power supply 18 maybe of lapracticable size and yet have an upper limit of sutiicient proportionsto produce an upper grid current magnitude at least as great as thatcorresponding to cut-off. The grid current may hence be varied over awide range of lmagnitudes by adjustment of knob 22 or rheostat 23 tocorrespondingly vary particle iiow through the grid 11 from a maximum atzero grid current to zero at cut-off grid current.

Regarding further the grid action of the present invention, it is notedthat the grid action on approaching charged particles is the sameregardless of particle polarfity. Thus the grid impartially controls thepassage of charged particles regardless of the charge polarity therefof.Even though the direction of deflection of positively :and negativelycharged particles is opposite upon enter- :ing the grid eld, yet thesame result is obtained insofar las the grid action is concerned, forparticles of either polarity are deflected not to pass through the grid.

It is to be noted that the particular coniiguration shown in Fig. l isonly illustrative of the present invention and a multitude of differentgrid wire coniigurations are possible. in this respect, reference ismade to Fig. 3 wherein a grid '31 .is illustrated as comprising a singlefolded grid wire 32 having a zigzag configuration. This grid 31 hasalternate portions or sections of the wire thereof extending insubstantially opposite 4directions so that a current liowing through thegrid actually flows in opposite directions in space through adjacentgrid sections. Grid energization is accomplished from a power supply 33connected through a switch '34 across the grid. With the particularcircuit shown herein, the grid would be effective only to gate adischarge in such 'as an ignitron or other tube. With the switch 34closed `a suicient current flows through the grid to establish arelatively strong magnetic field thereabout preventing the passage ofcharged particles therethrough. With the lswitch 34 open no gridenergization is provided so that the Vgrid exerts no influence uponcharged particles passing therethrough. With this circuitry a pulsedgrid operation is contemplated wherein a discharge is periodically gatedby the gri-d and the switch may, of cou-rse, comprise such as anelectronic valve controlled, for example, by some desired electricalphenomena associated with discharge passing through the grid. Althoughalternative circuitry is shown in Fig. 3, the grid structures of Figs. land 3 are equally operable with either illustrated circuit, `as well aswith other energizing and control circuits.

Considering now the manner in which the magnetic grid may be operativelyemployed in a gas iilled tube, eg., an ignitron, to effectuallyprecisely cut oli the tube or otherwise exert control over the dischargetherein, and referring to Fig. 4, there is provided therein an ignitron36 having a sealed low pressure envelope 37 of insulating material withan inwardly stepped anode supporting portion 38 at its top and are-entrant cathode pool forming portion 39 at its bottom end face. Ananode 41 is suspended transversely in the upper regions of the envelopeby means of an electrically conducting support rod42 extendinglongitudinally through portion 38 and externally Secured thereat to anelectrically conducting cap 43 engaging same. In the annulus formed atthe bottom of the envelope between re-entrant portion 39 and the outerwall of the envelope there is contained mercury, forming a cathode pool44. VAn igniter 46 is immersed in the pool and suspended by a lead-inconductor 47 secured thereto and leading exteriorly of the envelopethrough the recessed face of re-entrant portion 39. A lead-in conductor48 is immersed in the pool 44 and similarly led exteriorly of theenvelope through portion 39. All of the foregoing structural arrangementis conventional in ignitrons and the` ignitron 36 may be connected in acircuit in a conventional inanner to switch large amounts of current byconnection of the anode cap 43 to a more positive potential than thecathode lead-in conductor 48. A trigger pulse may then be applied toigniter lead-in conductor 47 to initiate conduction through the tube.Once conduction is established in the conventional ignitron, however,there is no provision for precisely gating off the tube, it Vbeingpossible to only terminate conduction in an unprecise manner by loweringthe anode potential. In addition, the amount of current flowing throughthe ignitron cannot be controlled other than by pre-selection of theconstants of the circuit in which employed. I'hese difficulties of aconventional ignitron arel overcome by a magnetic grid 49 in accordancewith theV present invention, e.g., similar to the zigzag grid 31previously described, disposed transversely of the ignitron envelope 37axially intermediate cathode pool 44and anode 41 in the path of thedischarge established therebetween upon pulsing of the igniter 46.More-specifically, the magnetic grid 49 may be secured in theabove-noted position within the envelope by fusing to the'interior wallsthereof or any other suitable attachment method familiar to thoseskilled in the tube art. The`ends of conductor 51 forming grid 49 areled exteriorlyv of the envelope `as shown at 52, 53 respectively, torfacilitate series connection of the grid in an energization circuit suchas either of those depicted in Figs l'or 3 and hereinbefore described.With the circuit ofFig. 3 connected to grid 49, for example, subsequentto initiation 0f `,conduction through the ignitron, the tube may begated off magnetically with substantial precision by the flow of acurrent pulse through the grid. Alternatively, with the circuit of Fig.1 employed with grid 49, the current flow through the ignitron may bevaried as desired in response to variation of the flow of magnetic fieldgenerating current through the magnetic grid.

As previously stated, the grid action of the present invention isdependent upon the establishment of magnetic fields that in whole or inpart deflect and ultimately repel approaching charged particles ofeither polarity. As seen from Fig. 3, it is not necessary that thefields be established by currents flowing exactly in parallel oppositionin space for satisfactory field congurations are possible with somewhatunparallel current fiow. With a greater grid wire displacement a largercurrent therethrough is, of course, required to produce a desiredmagnetic field strength half way between same and thus an increasedcurrent ow can be made to compensate for lack of parallelism in currentpaths, the term substantially parallel being herein employed toencompass those configurations such as illustrated in 1Fig. 3 whereinthe establishment of suitable fields are yet possible without exactlyparallel grid sections.

There has been described above a novel magnetic grid having a wide rangeof utility and a multitude of possible structural variations within thescope of the invention land thus it is not intended to limit the presentinvention by the foregoing description but instead reference is made tothe following claims for a precise definition of the invention.

What I claim is:

1. A magnetic grid for controlling charged particle discharge comprisingat least one low resistance grid Wire having more than two sectionsspaced apart and extending in substantially opposite directions in thesame plane with said grid Wire'adapted for electrical energization topass current therethrough of sufficient magnitude that magnetic fieldsestablished about adjacent sections of said wire deflect chargedparticles from the grid.

2. A magnetic grid comprising a uniplanar double spiral of lowresistance grid conductor with a first spiral turning inward to thecenter and a second spiral turning outward from connection to the firstspiral at the center thereof and spaced equally between turns of saidfirst spiral, and means forcing a controllable electric current throughsaid double spiral to establish magnetic fields thereabout that areadditive between adjacent grid conductors to deflect charged particlesapproaching the grid.

3.l A magnetic control grid for controlling the passage of chargedparticles comprising means defining a low resistance electrical currentpath with alternate spaced portions in opposite directions and in thesame plane, and means forcing a controllable electric current throughsaid path for establishing additive magnetic fields between adjacentportions thereof for defiecting approaching charged particles inproportion to the magnitude of current 'flow through the path, saidmeans having an upper controllable current limit of at least the currentcorresponding to magnetic deflection of all charged particles from pathsthrough the plane ofthe current path portions.

4. A magnetic control grid for controlling passage of charged particlescomprising folded conducting means defining opposed low resistanceelectric current paths in spaced substantially parallel disposition inthe same plane, power supply means connected to energize said conductingmeans, and control means for controllably pulsing the current flowthrough said conducting means and establishing a current pulse ofsuicient magnitude therein to magnetically gate ofi the passage ofparticles through the plane of the conducting means.

5. In an ignitron having at least a cathode pool and anode disposed atopposite ends of a sealed low pressure envelope with an igniter immersedin the cathode pool and separate input leads extending from the cathodepool, anode, and igniter exteriorly of the envelope, the combinationcomprising a magnetic control grid disposed transversely of the envelopeintermediate the cathode pool and anode and comprising folded conductingmeans defining opposed low resistance electric current paths in spacedsubstantially parallel disposition and in the same plane with each endof the conducting means leading exteriorly through said envelope forseries connection to a current source.

References Cited in the le of this patent UNITED STATES PATENTS

